sortCounters are updated inside SortedFileWriter::writeChunk(), which is called once per kSortedFileBufferSize write buffer flush. A single logical spill event that is triggered when the in-memory buffer reaches a memory limit of 100MB produces ~1600 chunk writes. As a result, spillToDisk overcounts spill events. Sort counters should be incremented once per logical spill. This is done already for the explain output where the spilledRanges are used.